/*------------------------------------------------------------------------- * * standby.c * Misc functions used in Hot Standby mode. * * All functions for handling RM_STANDBY_ID, which relate to * AccessExclusiveLocks and starting snapshots for Hot Standby mode. * Plus conflict recovery processing. * * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * * IDENTIFICATION * src/backend/storage/ipc/standby.c * *------------------------------------------------------------------------- */ #include "postgres.h" #include "access/transam.h" #include "access/twophase.h" #include "access/xact.h" #include "access/xlog.h" #include "access/xloginsert.h" #include "miscadmin.h" #include "pgstat.h" #include "storage/bufmgr.h" #include "storage/lmgr.h" #include "storage/proc.h" #include "storage/procarray.h" #include "storage/sinvaladt.h" #include "storage/standby.h" #include "utils/hsearch.h" #include "utils/memutils.h" #include "utils/ps_status.h" #include "utils/timeout.h" #include "utils/timestamp.h" /* User-settable GUC parameters */ int vacuum_defer_cleanup_age; int max_standby_archive_delay = 30 * 1000; int max_standby_streaming_delay = 30 * 1000; static HTAB *RecoveryLockLists; /* Flags set by timeout handlers */ static volatile sig_atomic_t got_standby_deadlock_timeout = false; static volatile sig_atomic_t got_standby_lock_timeout = false; static void ResolveRecoveryConflictWithVirtualXIDs(VirtualTransactionId *waitlist, ProcSignalReason reason, bool report_waiting); static void SendRecoveryConflictWithBufferPin(ProcSignalReason reason); static XLogRecPtr LogCurrentRunningXacts(RunningTransactions CurrRunningXacts); static void LogAccessExclusiveLocks(int nlocks, xl_standby_lock *locks); /* * Keep track of all the locks owned by a given transaction. */ typedef struct RecoveryLockListsEntry { TransactionId xid; List *locks; } RecoveryLockListsEntry; /* * InitRecoveryTransactionEnvironment * Initialize tracking of in-progress transactions in master * * We need to issue shared invalidations and hold locks. Holding locks * means others may want to wait on us, so we need to make a lock table * vxact entry like a real transaction. We could create and delete * lock table entries for each transaction but its simpler just to create * one permanent entry and leave it there all the time. Locks are then * acquired and released as needed. Yes, this means you can see the * Startup process in pg_locks once we have run this. */ void InitRecoveryTransactionEnvironment(void) { VirtualTransactionId vxid; HASHCTL hash_ctl; /* * Initialize the hash table for tracking the list of locks held by each * transaction. */ memset(&hash_ctl, 0, sizeof(hash_ctl)); hash_ctl.keysize = sizeof(TransactionId); hash_ctl.entrysize = sizeof(RecoveryLockListsEntry); RecoveryLockLists = hash_create("RecoveryLockLists", 64, &hash_ctl, HASH_ELEM | HASH_BLOBS); /* * Initialize shared invalidation management for Startup process, being * careful to register ourselves as a sendOnly process so we don't need to * read messages, nor will we get signalled when the queue starts filling * up. */ SharedInvalBackendInit(true); /* * Lock a virtual transaction id for Startup process. * * We need to do GetNextLocalTransactionId() because * SharedInvalBackendInit() leaves localTransactionid invalid and the lock * manager doesn't like that at all. * * Note that we don't need to run XactLockTableInsert() because nobody * needs to wait on xids. That sounds a little strange, but table locks * are held by vxids and row level locks are held by xids. All queries * hold AccessShareLocks so never block while we write or lock new rows. */ vxid.backendId = MyBackendId; vxid.localTransactionId = GetNextLocalTransactionId(); VirtualXactLockTableInsert(vxid); standbyState = STANDBY_INITIALIZED; } /* * ShutdownRecoveryTransactionEnvironment * Shut down transaction tracking * * Prepare to switch from hot standby mode to normal operation. Shut down * recovery-time transaction tracking. * * This must be called even in shutdown of startup process if transaction * tracking has been initialized. Otherwise some locks the tracked * transactions were holding will not be released and and may interfere with * the processes still running (but will exit soon later) at the exit of * startup process. */ void ShutdownRecoveryTransactionEnvironment(void) { /* * Do nothing if RecoveryLockLists is NULL because which means that * transaction tracking has not been yet initialized or has been already * shutdowned. This prevents transaction tracking from being shutdowned * unexpectedly more than once. */ if (RecoveryLockLists == NULL) return; /* Mark all tracked in-progress transactions as finished. */ ExpireAllKnownAssignedTransactionIds(); /* Release all locks the tracked transactions were holding */ StandbyReleaseAllLocks(); /* Destroy the hash table of locks. */ hash_destroy(RecoveryLockLists); RecoveryLockLists = NULL; /* Cleanup our VirtualTransaction */ VirtualXactLockTableCleanup(); } /* * ----------------------------------------------------- * Standby wait timers and backend cancel logic * ----------------------------------------------------- */ /* * Determine the cutoff time at which we want to start canceling conflicting * transactions. Returns zero (a time safely in the past) if we are willing * to wait forever. */ static TimestampTz GetStandbyLimitTime(void) { TimestampTz rtime; bool fromStream; /* * The cutoff time is the last WAL data receipt time plus the appropriate * delay variable. Delay of -1 means wait forever. */ GetXLogReceiptTime(&rtime, &fromStream); if (fromStream) { if (max_standby_streaming_delay < 0) return 0; /* wait forever */ return TimestampTzPlusMilliseconds(rtime, max_standby_streaming_delay); } else { if (max_standby_archive_delay < 0) return 0; /* wait forever */ return TimestampTzPlusMilliseconds(rtime, max_standby_archive_delay); } } #define STANDBY_INITIAL_WAIT_US 1000 static int standbyWait_us = STANDBY_INITIAL_WAIT_US; /* * Standby wait logic for ResolveRecoveryConflictWithVirtualXIDs. * We wait here for a while then return. If we decide we can't wait any * more then we return true, if we can wait some more return false. */ static bool WaitExceedsMaxStandbyDelay(void) { TimestampTz ltime; CHECK_FOR_INTERRUPTS(); /* Are we past the limit time? */ ltime = GetStandbyLimitTime(); if (ltime && GetCurrentTimestamp() >= ltime) return true; /* * Sleep a bit (this is essential to avoid busy-waiting). */ pg_usleep(standbyWait_us); /* * Progressively increase the sleep times, but not to more than 1s, since * pg_usleep isn't interruptable on some platforms. */ standbyWait_us *= 2; if (standbyWait_us > 1000000) standbyWait_us = 1000000; return false; } /* * This is the main executioner for any query backend that conflicts with * recovery processing. Judgement has already been passed on it within * a specific rmgr. Here we just issue the orders to the procs. The procs * then throw the required error as instructed. * * If report_waiting is true, "waiting" is reported in PS display if necessary. * If the caller has already reported that, report_waiting should be false. * Otherwise, "waiting" is reported twice unexpectedly. */ static void ResolveRecoveryConflictWithVirtualXIDs(VirtualTransactionId *waitlist, ProcSignalReason reason, bool report_waiting) { TimestampTz waitStart = 0; char *new_status; /* Fast exit, to avoid a kernel call if there's no work to be done. */ if (!VirtualTransactionIdIsValid(*waitlist)) return; if (report_waiting) waitStart = GetCurrentTimestamp(); new_status = NULL; /* we haven't changed the ps display */ while (VirtualTransactionIdIsValid(*waitlist)) { /* reset standbyWait_us for each xact we wait for */ standbyWait_us = STANDBY_INITIAL_WAIT_US; /* wait until the virtual xid is gone */ while (!VirtualXactLock(*waitlist, false)) { /* * Report via ps if we have been waiting for more than 500 msec * (should that be configurable?) */ if (update_process_title && new_status == NULL && report_waiting && TimestampDifferenceExceeds(waitStart, GetCurrentTimestamp(), 500)) { const char *old_status; int len; old_status = get_ps_display(&len); new_status = (char *) palloc(len + 8 + 1); memcpy(new_status, old_status, len); strcpy(new_status + len, " waiting"); set_ps_display(new_status, false); new_status[len] = '\0'; /* truncate off " waiting" */ } /* Is it time to kill it? */ if (WaitExceedsMaxStandbyDelay()) { pid_t pid; /* * Now find out who to throw out of the balloon. */ Assert(VirtualTransactionIdIsValid(*waitlist)); pid = CancelVirtualTransaction(*waitlist, reason); /* * Wait a little bit for it to die so that we avoid flooding * an unresponsive backend when system is heavily loaded. */ if (pid != 0) pg_usleep(5000L); } } /* The virtual transaction is gone now, wait for the next one */ waitlist++; } /* Reset ps display if we changed it */ if (new_status) { set_ps_display(new_status, false); pfree(new_status); } } void ResolveRecoveryConflictWithSnapshot(TransactionId latestRemovedXid, RelFileNode node) { VirtualTransactionId *backends; /* * If we get passed InvalidTransactionId then we are a little surprised, * but it is theoretically possible in normal running. It also happens * when replaying already applied WAL records after a standby crash or * restart, or when replaying an XLOG_HEAP2_VISIBLE record that marks as * frozen a page which was already all-visible. If latestRemovedXid is * invalid then there is no conflict. That rule applies across all record * types that suffer from this conflict. */ if (!TransactionIdIsValid(latestRemovedXid)) return; backends = GetConflictingVirtualXIDs(latestRemovedXid, node.dbNode); ResolveRecoveryConflictWithVirtualXIDs(backends, PROCSIG_RECOVERY_CONFLICT_SNAPSHOT, true); } void ResolveRecoveryConflictWithTablespace(Oid tsid) { VirtualTransactionId *temp_file_users; /* * Standby users may be currently using this tablespace for their * temporary files. We only care about current users because * temp_tablespace parameter will just ignore tablespaces that no longer * exist. * * Ask everybody to cancel their queries immediately so we can ensure no * temp files remain and we can remove the tablespace. Nuke the entire * site from orbit, it's the only way to be sure. * * XXX: We could work out the pids of active backends using this * tablespace by examining the temp filenames in the directory. We would * then convert the pids into VirtualXIDs before attempting to cancel * them. * * We don't wait for commit because drop tablespace is non-transactional. */ temp_file_users = GetConflictingVirtualXIDs(InvalidTransactionId, InvalidOid); ResolveRecoveryConflictWithVirtualXIDs(temp_file_users, PROCSIG_RECOVERY_CONFLICT_TABLESPACE, true); } void ResolveRecoveryConflictWithDatabase(Oid dbid) { /* * We don't do ResolveRecoveryConflictWithVirtualXIDs() here since that * only waits for transactions and completely idle sessions would block * us. This is rare enough that we do this as simply as possible: no wait, * just force them off immediately. * * No locking is required here because we already acquired * AccessExclusiveLock. Anybody trying to connect while we do this will * block during InitPostgres() and then disconnect when they see the * database has been removed. */ while (CountDBBackends(dbid) > 0) { CancelDBBackends(dbid, PROCSIG_RECOVERY_CONFLICT_DATABASE, true); /* * Wait awhile for them to die so that we avoid flooding an * unresponsive backend when system is heavily loaded. */ pg_usleep(10000); } } /* * ResolveRecoveryConflictWithLock is called from ProcSleep() * to resolve conflicts with other backends holding relation locks. * * The WaitLatch sleep normally done in ProcSleep() * (when not InHotStandby) is performed here, for code clarity. * * We either resolve conflicts immediately or set a timeout to wake us at * the limit of our patience. * * Resolve conflicts by canceling to all backends holding a conflicting * lock. As we are already queued to be granted the lock, no new lock * requests conflicting with ours will be granted in the meantime. * * We also must check for deadlocks involving the Startup process and * hot-standby backend processes. If deadlock_timeout is reached in * this function, all the backends holding the conflicting locks are * requested to check themselves for deadlocks. */ void ResolveRecoveryConflictWithLock(LOCKTAG locktag) { TimestampTz ltime; Assert(InHotStandby); ltime = GetStandbyLimitTime(); if (GetCurrentTimestamp() >= ltime && ltime != 0) { /* * We're already behind, so clear a path as quickly as possible. */ VirtualTransactionId *backends; backends = GetLockConflicts(&locktag, AccessExclusiveLock); /* * Prevent ResolveRecoveryConflictWithVirtualXIDs() from reporting * "waiting" in PS display by disabling its argument report_waiting * because the caller, WaitOnLock(), has already reported that. */ ResolveRecoveryConflictWithVirtualXIDs(backends, PROCSIG_RECOVERY_CONFLICT_LOCK, false); } else { /* * Wait (or wait again) until ltime, and check for deadlocks as well * if we will be waiting longer than deadlock_timeout */ EnableTimeoutParams timeouts[2]; int cnt = 0; if (ltime != 0) { got_standby_lock_timeout = false; timeouts[cnt].id = STANDBY_LOCK_TIMEOUT; timeouts[cnt].type = TMPARAM_AT; timeouts[cnt].fin_time = ltime; cnt++; } got_standby_deadlock_timeout = false; timeouts[cnt].id = STANDBY_DEADLOCK_TIMEOUT; timeouts[cnt].type = TMPARAM_AFTER; timeouts[cnt].delay_ms = DeadlockTimeout; cnt++; enable_timeouts(timeouts, cnt); } /* Wait to be signaled by the release of the Relation Lock */ ProcWaitForSignal(PG_WAIT_LOCK | locktag.locktag_type); /* * Exit if ltime is reached. Then all the backends holding conflicting * locks will be canceled in the next ResolveRecoveryConflictWithLock() * call. */ if (got_standby_lock_timeout) goto cleanup; if (got_standby_deadlock_timeout) { VirtualTransactionId *backends; backends = GetLockConflicts(&locktag, AccessExclusiveLock); /* Quick exit if there's no work to be done */ if (!VirtualTransactionIdIsValid(*backends)) goto cleanup; /* * Send signals to all the backends holding the conflicting locks, to * ask them to check themselves for deadlocks. */ while (VirtualTransactionIdIsValid(*backends)) { SignalVirtualTransaction(*backends, PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK, false); backends++; } /* * Wait again here to be signaled by the release of the Relation Lock, * to prevent the subsequent RecoveryConflictWithLock() from causing * deadlock_timeout and sending a request for deadlocks check again. * Otherwise the request continues to be sent every deadlock_timeout * until the relation locks are released or ltime is reached. */ got_standby_deadlock_timeout = false; ProcWaitForSignal(PG_WAIT_LOCK | locktag.locktag_type); } cleanup: /* * Clear any timeout requests established above. We assume here that the * Startup process doesn't have any other outstanding timeouts than those * used by this function. If that stops being true, we could cancel the * timeouts individually, but that'd be slower. */ disable_all_timeouts(false); got_standby_lock_timeout = false; got_standby_deadlock_timeout = false; } /* * ResolveRecoveryConflictWithBufferPin is called from LockBufferForCleanup() * to resolve conflicts with other backends holding buffer pins. * * The ProcWaitForSignal() sleep normally done in LockBufferForCleanup() * (when not InHotStandby) is performed here, for code clarity. * * We either resolve conflicts immediately or set a timeout to wake us at * the limit of our patience. * * Resolve conflicts by sending a PROCSIG signal to all backends to check if * they hold one of the buffer pins that is blocking Startup process. If so, * those backends will take an appropriate error action, ERROR or FATAL. * * We also must check for deadlocks. Deadlocks occur because if queries * wait on a lock, that must be behind an AccessExclusiveLock, which can only * be cleared if the Startup process replays a transaction completion record. * If Startup process is also waiting then that is a deadlock. The deadlock * can occur if the query is waiting and then the Startup sleeps, or if * Startup is sleeping and the query waits on a lock. We protect against * only the former sequence here, the latter sequence is checked prior to * the query sleeping, in CheckRecoveryConflictDeadlock(). * * Deadlocks are extremely rare, and relatively expensive to check for, * so we don't do a deadlock check right away ... only if we have had to wait * at least deadlock_timeout. */ void ResolveRecoveryConflictWithBufferPin(void) { TimestampTz ltime; Assert(InHotStandby); ltime = GetStandbyLimitTime(); if (GetCurrentTimestamp() >= ltime && ltime != 0) { /* * We're already behind, so clear a path as quickly as possible. */ SendRecoveryConflictWithBufferPin(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN); } else { /* * Wake up at ltime, and check for deadlocks as well if we will be * waiting longer than deadlock_timeout */ EnableTimeoutParams timeouts[2]; int cnt = 0; if (ltime != 0) { timeouts[cnt].id = STANDBY_TIMEOUT; timeouts[cnt].type = TMPARAM_AT; timeouts[cnt].fin_time = ltime; cnt++; } got_standby_deadlock_timeout = false; timeouts[cnt].id = STANDBY_DEADLOCK_TIMEOUT; timeouts[cnt].type = TMPARAM_AFTER; timeouts[cnt].delay_ms = DeadlockTimeout; cnt++; enable_timeouts(timeouts, cnt); } /* Wait to be signaled by UnpinBuffer() */ ProcWaitForSignal(PG_WAIT_BUFFER_PIN); if (got_standby_deadlock_timeout) { /* * Send out a request for hot-standby backends to check themselves for * deadlocks. * * XXX The subsequent ResolveRecoveryConflictWithBufferPin() will wait * to be signaled by UnpinBuffer() again and send a request for * deadlocks check if deadlock_timeout happens. This causes the * request to continue to be sent every deadlock_timeout until the * buffer is unpinned or ltime is reached. This would increase the * workload in the startup process and backends. In practice it may * not be so harmful because the period that the buffer is kept pinned * is basically no so long. But we should fix this? */ SendRecoveryConflictWithBufferPin( PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK); } /* * Clear any timeout requests established above. We assume here that the * Startup process doesn't have any other timeouts than what this function * uses. If that stops being true, we could cancel the timeouts * individually, but that'd be slower. */ disable_all_timeouts(false); got_standby_deadlock_timeout = false; } static void SendRecoveryConflictWithBufferPin(ProcSignalReason reason) { Assert(reason == PROCSIG_RECOVERY_CONFLICT_BUFFERPIN || reason == PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK); /* * We send signal to all backends to ask them if they are holding the * buffer pin which is delaying the Startup process. We must not set the * conflict flag yet, since most backends will be innocent. Let the * SIGUSR1 handling in each backend decide their own fate. */ CancelDBBackends(InvalidOid, reason, false); } /* * In Hot Standby perform early deadlock detection. We abort the lock * wait if we are about to sleep while holding the buffer pin that Startup * process is waiting for. * * Note: this code is pessimistic, because there is no way for it to * determine whether an actual deadlock condition is present: the lock we * need to wait for might be unrelated to any held by the Startup process. * Sooner or later, this mechanism should get ripped out in favor of somehow * accounting for buffer locks in DeadLockCheck(). However, errors here * seem to be very low-probability in practice, so for now it's not worth * the trouble. */ void CheckRecoveryConflictDeadlock(void) { Assert(!InRecovery); /* do not call in Startup process */ if (!HoldingBufferPinThatDelaysRecovery()) return; /* * Error message should match ProcessInterrupts() but we avoid calling * that because we aren't handling an interrupt at this point. Note that * we only cancel the current transaction here, so if we are in a * subtransaction and the pin is held by a parent, then the Startup * process will continue to wait even though we have avoided deadlock. */ ereport(ERROR, (errcode(ERRCODE_T_R_DEADLOCK_DETECTED), errmsg("canceling statement due to conflict with recovery"), errdetail("User transaction caused buffer deadlock with recovery."))); } /* -------------------------------- * timeout handler routines * -------------------------------- */ /* * StandbyDeadLockHandler() will be called if STANDBY_DEADLOCK_TIMEOUT * occurs before STANDBY_TIMEOUT. */ void StandbyDeadLockHandler(void) { got_standby_deadlock_timeout = true; } /* * StandbyTimeoutHandler() will be called if STANDBY_TIMEOUT is exceeded. * Send out a request to release conflicting buffer pins unconditionally, * so we can press ahead with applying changes in recovery. */ void StandbyTimeoutHandler(void) { /* forget any pending STANDBY_DEADLOCK_TIMEOUT request */ disable_timeout(STANDBY_DEADLOCK_TIMEOUT, false); SendRecoveryConflictWithBufferPin(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN); } /* * StandbyLockTimeoutHandler() will be called if STANDBY_LOCK_TIMEOUT is exceeded. */ void StandbyLockTimeoutHandler(void) { got_standby_lock_timeout = true; } /* * ----------------------------------------------------- * Locking in Recovery Mode * ----------------------------------------------------- * * All locks are held by the Startup process using a single virtual * transaction. This implementation is both simpler and in some senses, * more correct. The locks held mean "some original transaction held * this lock, so query access is not allowed at this time". So the Startup * process is the proxy by which the original locks are implemented. * * We only keep track of AccessExclusiveLocks, which are only ever held by * one transaction on one relation. * * We keep a hash table of lists of locks in local memory keyed by xid, * RecoveryLockLists, so we can keep track of the various entries made by * the Startup process's virtual xid in the shared lock table. * * List elements use type xl_standby_lock, since the WAL record type exactly * matches the information that we need to keep track of. * * We use session locks rather than normal locks so we don't need * ResourceOwners. */ void StandbyAcquireAccessExclusiveLock(TransactionId xid, Oid dbOid, Oid relOid) { RecoveryLockListsEntry *entry; xl_standby_lock *newlock; LOCKTAG locktag; bool found; /* Already processed? */ if (!TransactionIdIsValid(xid) || TransactionIdDidCommit(xid) || TransactionIdDidAbort(xid)) return; elog(trace_recovery(DEBUG4), "adding recovery lock: db %u rel %u", dbOid, relOid); /* dbOid is InvalidOid when we are locking a shared relation. */ Assert(OidIsValid(relOid)); /* Create a new list for this xid, if we don't have one already. */ entry = hash_search(RecoveryLockLists, &xid, HASH_ENTER, &found); if (!found) { entry->xid = xid; entry->locks = NIL; } newlock = palloc(sizeof(xl_standby_lock)); newlock->xid = xid; newlock->dbOid = dbOid; newlock->relOid = relOid; entry->locks = lappend(entry->locks, newlock); SET_LOCKTAG_RELATION(locktag, newlock->dbOid, newlock->relOid); (void) LockAcquire(&locktag, AccessExclusiveLock, true, false); } static void StandbyReleaseLockList(List *locks) { while (locks) { xl_standby_lock *lock = (xl_standby_lock *) linitial(locks); LOCKTAG locktag; elog(trace_recovery(DEBUG4), "releasing recovery lock: xid %u db %u rel %u", lock->xid, lock->dbOid, lock->relOid); SET_LOCKTAG_RELATION(locktag, lock->dbOid, lock->relOid); if (!LockRelease(&locktag, AccessExclusiveLock, true)) { elog(LOG, "RecoveryLockLists contains entry for lock no longer recorded by lock manager: xid %u database %u relation %u", lock->xid, lock->dbOid, lock->relOid); Assert(false); } pfree(lock); locks = list_delete_first(locks); } } static void StandbyReleaseLocks(TransactionId xid) { RecoveryLockListsEntry *entry; if (TransactionIdIsValid(xid)) { if ((entry = hash_search(RecoveryLockLists, &xid, HASH_FIND, NULL))) { StandbyReleaseLockList(entry->locks); hash_search(RecoveryLockLists, entry, HASH_REMOVE, NULL); } } else StandbyReleaseAllLocks(); } /* * Release locks for a transaction tree, starting at xid down, from * RecoveryLockLists. * * Called during WAL replay of COMMIT/ROLLBACK when in hot standby mode, * to remove any AccessExclusiveLocks requested by a transaction. */ void StandbyReleaseLockTree(TransactionId xid, int nsubxids, TransactionId *subxids) { int i; StandbyReleaseLocks(xid); for (i = 0; i < nsubxids; i++) StandbyReleaseLocks(subxids[i]); } /* * Called at end of recovery and when we see a shutdown checkpoint. */ void StandbyReleaseAllLocks(void) { HASH_SEQ_STATUS status; RecoveryLockListsEntry *entry; elog(trace_recovery(DEBUG2), "release all standby locks"); hash_seq_init(&status, RecoveryLockLists); while ((entry = hash_seq_search(&status))) { StandbyReleaseLockList(entry->locks); hash_search(RecoveryLockLists, entry, HASH_REMOVE, NULL); } } /* * StandbyReleaseOldLocks * Release standby locks held by top-level XIDs that aren't running, * as long as they're not prepared transactions. */ void StandbyReleaseOldLocks(int nxids, TransactionId *xids) { HASH_SEQ_STATUS status; RecoveryLockListsEntry *entry; hash_seq_init(&status, RecoveryLockLists); while ((entry = hash_seq_search(&status))) { bool remove = false; Assert(TransactionIdIsValid(entry->xid)); if (StandbyTransactionIdIsPrepared(entry->xid)) remove = false; else { int i; bool found = false; for (i = 0; i < nxids; i++) { if (entry->xid == xids[i]) { found = true; break; } } /* * If its not a running transaction, remove it. */ if (!found) remove = true; } if (remove) { StandbyReleaseLockList(entry->locks); hash_search(RecoveryLockLists, entry, HASH_REMOVE, NULL); } } } /* * -------------------------------------------------------------------- * Recovery handling for Rmgr RM_STANDBY_ID * * These record types will only be created if XLogStandbyInfoActive() * -------------------------------------------------------------------- */ void standby_redo(XLogReaderState *record) { uint8 info = XLogRecGetInfo(record) & ~XLR_INFO_MASK; /* Backup blocks are not used in standby records */ Assert(!XLogRecHasAnyBlockRefs(record)); /* Do nothing if we're not in hot standby mode */ if (standbyState == STANDBY_DISABLED) return; if (info == XLOG_STANDBY_LOCK) { xl_standby_locks *xlrec = (xl_standby_locks *) XLogRecGetData(record); int i; for (i = 0; i < xlrec->nlocks; i++) StandbyAcquireAccessExclusiveLock(xlrec->locks[i].xid, xlrec->locks[i].dbOid, xlrec->locks[i].relOid); } else if (info == XLOG_RUNNING_XACTS) { xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record); RunningTransactionsData running; running.xcnt = xlrec->xcnt; running.subxcnt = xlrec->subxcnt; running.subxid_overflow = xlrec->subxid_overflow; running.nextXid = xlrec->nextXid; running.latestCompletedXid = xlrec->latestCompletedXid; running.oldestRunningXid = xlrec->oldestRunningXid; running.xids = xlrec->xids; ProcArrayApplyRecoveryInfo(&running); } else if (info == XLOG_INVALIDATIONS) { xl_invalidations *xlrec = (xl_invalidations *) XLogRecGetData(record); ProcessCommittedInvalidationMessages(xlrec->msgs, xlrec->nmsgs, xlrec->relcacheInitFileInval, xlrec->dbId, xlrec->tsId); } else elog(PANIC, "standby_redo: unknown op code %u", info); } /* * Log details of the current snapshot to WAL. This allows the snapshot state * to be reconstructed on the standby and for logical decoding. * * This is used for Hot Standby as follows: * * We can move directly to STANDBY_SNAPSHOT_READY at startup if we * start from a shutdown checkpoint because we know nothing was running * at that time and our recovery snapshot is known empty. In the more * typical case of an online checkpoint we need to jump through a few * hoops to get a correct recovery snapshot and this requires a two or * sometimes a three stage process. * * The initial snapshot must contain all running xids and all current * AccessExclusiveLocks at a point in time on the standby. Assembling * that information while the server is running requires many and * various LWLocks, so we choose to derive that information piece by * piece and then re-assemble that info on the standby. When that * information is fully assembled we move to STANDBY_SNAPSHOT_READY. * * Since locking on the primary when we derive the information is not * strict, we note that there is a time window between the derivation and * writing to WAL of the derived information. That allows race conditions * that we must resolve, since xids and locks may enter or leave the * snapshot during that window. This creates the issue that an xid or * lock may start *after* the snapshot has been derived yet *before* the * snapshot is logged in the running xacts WAL record. We resolve this by * starting to accumulate changes at a point just prior to when we derive * the snapshot on the primary, then ignore duplicates when we later apply * the snapshot from the running xacts record. This is implemented during * CreateCheckpoint() where we use the logical checkpoint location as * our starting point and then write the running xacts record immediately * before writing the main checkpoint WAL record. Since we always start * up from a checkpoint and are immediately at our starting point, we * unconditionally move to STANDBY_INITIALIZED. After this point we * must do 4 things: * * move shared nextXid forwards as we see new xids * * extend the clog and subtrans with each new xid * * keep track of uncommitted known assigned xids * * keep track of uncommitted AccessExclusiveLocks * * When we see a commit/abort we must remove known assigned xids and locks * from the completing transaction. Attempted removals that cannot locate * an entry are expected and must not cause an error when we are in state * STANDBY_INITIALIZED. This is implemented in StandbyReleaseLocks() and * KnownAssignedXidsRemove(). * * Later, when we apply the running xact data we must be careful to ignore * transactions already committed, since those commits raced ahead when * making WAL entries. * * The loose timing also means that locks may be recorded that have a * zero xid, since xids are removed from procs before locks are removed. * So we must prune the lock list down to ensure we hold locks only for * currently running xids, performed by StandbyReleaseOldLocks(). * Zero xids should no longer be possible, but we may be replaying WAL * from a time when they were possible. * * For logical decoding only the running xacts information is needed; * there's no need to look at the locking information, but it's logged anyway, * as there's no independent knob to just enable logical decoding. For * details of how this is used, check snapbuild.c's introductory comment. * * * Returns the RecPtr of the last inserted record. */ XLogRecPtr LogStandbySnapshot(void) { XLogRecPtr recptr; RunningTransactions running; xl_standby_lock *locks; int nlocks; Assert(XLogStandbyInfoActive()); /* * Get details of any AccessExclusiveLocks being held at the moment. */ locks = GetRunningTransactionLocks(&nlocks); if (nlocks > 0) LogAccessExclusiveLocks(nlocks, locks); pfree(locks); /* * Log details of all in-progress transactions. This should be the last * record we write, because standby will open up when it sees this. */ running = GetRunningTransactionData(); /* * GetRunningTransactionData() acquired ProcArrayLock, we must release it. * For Hot Standby this can be done before inserting the WAL record * because ProcArrayApplyRecoveryInfo() rechecks the commit status using * the clog. For logical decoding, though, the lock can't be released * early because the clog might be "in the future" from the POV of the * historic snapshot. This would allow for situations where we're waiting * for the end of a transaction listed in the xl_running_xacts record * which, according to the WAL, has committed before the xl_running_xacts * record. Fortunately this routine isn't executed frequently, and it's * only a shared lock. */ if (wal_level < WAL_LEVEL_LOGICAL) LWLockRelease(ProcArrayLock); recptr = LogCurrentRunningXacts(running); /* Release lock if we kept it longer ... */ if (wal_level >= WAL_LEVEL_LOGICAL) LWLockRelease(ProcArrayLock); /* GetRunningTransactionData() acquired XidGenLock, we must release it */ LWLockRelease(XidGenLock); return recptr; } /* * Record an enhanced snapshot of running transactions into WAL. * * The definitions of RunningTransactionsData and xl_xact_running_xacts are * similar. We keep them separate because xl_xact_running_xacts is a * contiguous chunk of memory and never exists fully until it is assembled in * WAL. The inserted records are marked as not being important for durability, * to avoid triggering superfluous checkpoint / archiving activity. */ static XLogRecPtr LogCurrentRunningXacts(RunningTransactions CurrRunningXacts) { xl_running_xacts xlrec; XLogRecPtr recptr; xlrec.xcnt = CurrRunningXacts->xcnt; xlrec.subxcnt = CurrRunningXacts->subxcnt; xlrec.subxid_overflow = CurrRunningXacts->subxid_overflow; xlrec.nextXid = CurrRunningXacts->nextXid; xlrec.oldestRunningXid = CurrRunningXacts->oldestRunningXid; xlrec.latestCompletedXid = CurrRunningXacts->latestCompletedXid; /* Header */ XLogBeginInsert(); XLogSetRecordFlags(XLOG_MARK_UNIMPORTANT); XLogRegisterData((char *) (&xlrec), MinSizeOfXactRunningXacts); /* array of TransactionIds */ if (xlrec.xcnt > 0) XLogRegisterData((char *) CurrRunningXacts->xids, (xlrec.xcnt + xlrec.subxcnt) * sizeof(TransactionId)); recptr = XLogInsert(RM_STANDBY_ID, XLOG_RUNNING_XACTS); if (CurrRunningXacts->subxid_overflow) elog(trace_recovery(DEBUG2), "snapshot of %u running transactions overflowed (lsn %X/%X oldest xid %u latest complete %u next xid %u)", CurrRunningXacts->xcnt, (uint32) (recptr >> 32), (uint32) recptr, CurrRunningXacts->oldestRunningXid, CurrRunningXacts->latestCompletedXid, CurrRunningXacts->nextXid); else elog(trace_recovery(DEBUG2), "snapshot of %u+%u running transaction ids (lsn %X/%X oldest xid %u latest complete %u next xid %u)", CurrRunningXacts->xcnt, CurrRunningXacts->subxcnt, (uint32) (recptr >> 32), (uint32) recptr, CurrRunningXacts->oldestRunningXid, CurrRunningXacts->latestCompletedXid, CurrRunningXacts->nextXid); /* * Ensure running_xacts information is synced to disk not too far in the * future. We don't want to stall anything though (i.e. use XLogFlush()), * so we let the wal writer do it during normal operation. * XLogSetAsyncXactLSN() conveniently will mark the LSN as to-be-synced * and nudge the WALWriter into action if sleeping. Check * XLogBackgroundFlush() for details why a record might not be flushed * without it. */ XLogSetAsyncXactLSN(recptr); return recptr; } /* * Wholesale logging of AccessExclusiveLocks. Other lock types need not be * logged, as described in backend/storage/lmgr/README. */ static void LogAccessExclusiveLocks(int nlocks, xl_standby_lock *locks) { xl_standby_locks xlrec; xlrec.nlocks = nlocks; XLogBeginInsert(); XLogRegisterData((char *) &xlrec, offsetof(xl_standby_locks, locks)); XLogRegisterData((char *) locks, nlocks * sizeof(xl_standby_lock)); XLogSetRecordFlags(XLOG_MARK_UNIMPORTANT); (void) XLogInsert(RM_STANDBY_ID, XLOG_STANDBY_LOCK); } /* * Individual logging of AccessExclusiveLocks for use during LockAcquire() */ void LogAccessExclusiveLock(Oid dbOid, Oid relOid) { xl_standby_lock xlrec; xlrec.xid = GetCurrentTransactionId(); /* * Decode the locktag back to the original values, to avoid sending lots * of empty bytes with every message. See lock.h to check how a locktag * is defined for LOCKTAG_RELATION */ xlrec.dbOid = dbOid; xlrec.relOid = relOid; LogAccessExclusiveLocks(1, &xlrec); MyXactFlags |= XACT_FLAGS_ACQUIREDACCESSEXCLUSIVELOCK; } /* * Prepare to log an AccessExclusiveLock, for use during LockAcquire() */ void LogAccessExclusiveLockPrepare(void) { /* * Ensure that a TransactionId has been assigned to this transaction, for * two reasons, both related to lock release on the standby. First, we * must assign an xid so that RecordTransactionCommit() and * RecordTransactionAbort() do not optimise away the transaction * completion record which recovery relies upon to release locks. It's a * hack, but for a corner case not worth adding code for into the main * commit path. Second, we must assign an xid before the lock is recorded * in shared memory, otherwise a concurrently executing * GetRunningTransactionLocks() might see a lock associated with an * InvalidTransactionId which we later assert cannot happen. */ (void) GetCurrentTransactionId(); } /* * Emit WAL for invalidations. This currently is only used for commits without * an xid but which contain invalidations. */ void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs, bool relcacheInitFileInval) { xl_invalidations xlrec; /* prepare record */ memset(&xlrec, 0, sizeof(xlrec)); xlrec.dbId = MyDatabaseId; xlrec.tsId = MyDatabaseTableSpace; xlrec.relcacheInitFileInval = relcacheInitFileInval; xlrec.nmsgs = nmsgs; /* perform insertion */ XLogBeginInsert(); XLogRegisterData((char *) (&xlrec), MinSizeOfInvalidations); XLogRegisterData((char *) msgs, nmsgs * sizeof(SharedInvalidationMessage)); XLogInsert(RM_STANDBY_ID, XLOG_INVALIDATIONS); }